Most of the vector supercomputer manufacturers
produce multiprocessor systems based on their vector processors.
Since a single node is so expensive and so finely tuned to memory
bandwidth and other architectural parameters, the multiprocessor
configurations have only a few processors. The largest currently
is the Cray C-90, which has up to 16 processors.

An 8-processor
Cray Y-MP is a shared memory MIMD system in the style of the BBN
Butterfly, with processors connected to a set of memories via a
multistage switching network. The switching network is a 3-level
crossbar. A major difference between the switching networks in
the Butterfly and Y-MP is that in the Y-MP there are many more
memory modules than processors since the individual processors
were designed to connect to an interleaved memory. There are
enough memory modules - 32 per processor - and enough
flexibility
in the switch to allow each processor to connect to several banks
at once so it can transfer vectors into and out of vector
registers at a rate of one item per clock cycle. The assignment
of virtual addresses to memory modules differs from the Butterfly
arrangement, also, since in the interleaved organization
consecutive addresses need to be in different modules. An
exception to the rule that few processors are used in
multiprocessor vector machines is a 222-processor system recently
announced by Fujitsu. The nodes in this machine will be
interconnected via a large, single-stage crossbar switch. Each
node in the system consists of a local interleaved memory, a
scalar processing unit, and a vector processing unit. The network
interface implements a single address space from the individual
local memories. Each node in the VPP500 will have a peak
performance of about 1.5 GFLOPS, so a full 222 processor system
will have a theoretical peak performance of over 300 GFLOPS.